1. Field of the Invention
This invention relates to eleotrodeposition of chromium for functional purposes on basic metals from hexavalent chromium plating baths containing an alkyl sulfonic acid, and, more particularly, it is concerned with a method of treating a chromium electroplating bath which contains an alkyl sulfonic acid to prevent heavy lead dioxide scale build-up on lead or lead alloy anodes used therein.
2. Description of the Prior Art
Hexavalent chromium electroplating baths containing an alkyl sulfonic acid produce non-iridescent, adherent, bright chromium deposits at high cathode efficiencies. Such baths, are described by Chessin and Newby in U.S. Pat. No. 4,588,481. They generally contain chromic acid as the source of chromium and sulfate as a catalyst and almost invariably employ lead or a lead alloy as the anode. However, in the presence of the alkyl sulfonic acid additive, it is often observed that such baths promote a rapid build-up of heavy lead dioxide scale on the anode, which is detrimental to the process. for example, a scale deposit of 150" to 174" in 2-3 days of electroplating may be experienced with these baths. When such scale is formed, it is necessary to interrupt the operation to clean the anodes. Furthermore, the anode life is significantly shortened when scale is found.
Accordingly, it is an object of the present invention to provide a method of treating a chromium electroplating bath which contains an alkyl sulfonic acid to prevent heavy scale build-up on lead or lead alloy anodes used therein.
A specific object of the invention is to provide a method of treating a chromium electroplating bath, which contains chromic acid, sulfate and methane sulfonic acid, to prevent heavy formation of lead dioxide on lead or lead alloy anodes used therein.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.